This invention relates to rechargeable batteries and small cell formation, and in particular to a method and system for charging and testing batteries that includes a semi-automatic calibration system operably connected thereto. The calibration system calibrates the charging and test system to provide increased reliability and accuracy during subsequent testing, measurement and control of battery current and voltage. The charging and test system is capable of simultaneous charging and testing of a plurality of battery cell assemblies. The charging and test system connects to the individual cells through a plurality of charging and data acquisition channels connected to a plurality of coaxial pin assemblies that have separated inner and outer conductors. These pins utilize a spring clip connector that performs the functions of mechanical retention and electrical connection. The spring clip connectors can be quickly and easily disconnected so that each individual pin assembly can be easily replaced when worn out or damaged. One embodiment of the present invention includes a calibration tray that is operably connected to the charging and testing system in place of a cell tray that holds the battery cells during charging and testing operations.
Rechargeable or galvanic batteries generally include an assembly of one or more electrochemical cells that convert energy produced by chemical reactions within the cells into low voltage, direct current electric energy. Each cell contains a cathode (positive electrode), an anode (negative electrode) and an electrolyte. When the cells are initially manufactured by placing the cathode, anode and electrolyte inside the cell case, charging equipment is used to apply a precisely controlled unidirectional current through the cell, from the cathode to the anode. This current produces an electrochemical reaction that converts the cathode, anode and electrolyte into chemical compounds that store energy for future use. This process may involve a plurality of time-varying current levels, including levels of zero current and/or current flow in the opposite direction (discharge). As is known to those skilled in the art, this process is referred to as formation.
After the cells undergo the formation process, the cells can be used to receive, store, generate and deliver electrical energy. As current is drawn from the battery, each cell is discharged. After discharge of a secondary battery, the original chemical state may be regained by recharging the cells. To reform the chemical reactants within the cell, a unidirectional charge current is applied to the electrodes of the battery in the opposite direction to that during discharge.
When manufacturing batteries utilizing cells of small size, such as those used in portable computing, telecommunication and electronic equipment, it is desirable to have a system to perform the formation process that can simultaneously process a large number of cells, maintain accurate control of the formation process of each cell at all times, and minimize the labor needed to load, connect, process, disconnect and unload these cells to and from the charging and testing equipment.
Normal manufacturing tolerances present in cell formation dictate that the charging and testing system must be capable of controlling the charging and testing processes for each cell on an individual basis, or a relatively small group of cells with respect to the total number of cells being processed at a given time. Therefore, it is desirable to develop a charging and test system that supports a plurality of data acquisition and control channels, with each channel being dedicated to one cell, or a relatively small group of cells.
It is further desirable to develop a method and system for battery charging and testing with semi-automatic calibration that is easily maintainable. In particular, the area that requires the most maintenance is the connection system to the cells. Secure connections of the cells to the charging and testing system is essential to maintain proper control of the formation and testing processes. The connections are subject to repeated cycling that can result in wear to the connection system. The connection system also is subject to the accumulation of contaminants that can interfere with the connection, and is exposed to a relatively significant risk of damage during normal use when cells are placed within and removed from the charging and testing system.
The performance capabilities of rechargeable batteries are evaluated and tested by computerized charging and testing equipment during and after manufacture to determine whether the batteries are performing in accordance with appropriate operational standards and design specifications. To evaluate the operational integrity of batteries, the testing equipment is programmed to measure the cell voltage and current under various conditions. Charging and testing equipment must be properly calibrated at all times to evaluate cell integrity and provide an accurate determination of electric energy needed to be applied to the cell to bring the operating characteristics of the cell into substantial agreement with appropriate standards for the battery. Traditionally, manual adjustment and calibration of the testing circuitry has been required to achieve compliance with process control and data acquisition requirements. However, manual adjustment of the circuitry is tedious and labor intensive because of the large number of inputs required (in general, one voltage input and one current input per cell) and high density packaging of equipment for each group of cells. Operator error can result in improper calibration of the testing equipment and inaccurate test results. Furthermore, when batteries are tested, proper calibration of the charging and testing equipment is essential to maintain the state of the charge within specific parameters for the cells. If the cell becomes overcharged, it may be damaged or even explode, causing damage to the charging and testing system and potential injury to the operator.
Therefore, it is desirable to develop an improved method and system for charging and testing circuitry used to form and evaluate multiple battery cells with minimal operator intervention under the control of a microprocessor. Such a charging and test system should provide accurate calibration of charging and testing circuitry for each cell to be tested. Because of the large number of battery cells routinely tested by the system, the charging and test system must have a durable construction, and preferably allow for quick and easy replacement of equipment used to connect the cells to the charging and testing equipment if such connecting equipment is damaged or becomes inoperable. This capability would facilitate the continuous operation of the charging and testing equipment and improve the efficiency of formation and testing procedures.